package jcode.code;


public class kmp {
    public static int KMP(String str, String sub, int pos) {
        if (str == null || sub == null)
            return -1;
        int lenStr = str.length();
        int lenSub = sub.length();
        if (lenStr == 0 || lenSub == 0)
            return -1;
        if (pos < 0 || pos >= lenStr)
            return -1;

        int[] next = new int[lenSub];
        getNext(sub, next);
        int i = pos;
        int j = 0;

        while (i < lenStr && j < lenSub) {
            if (j == -1 || str.charAt(i) == sub.charAt(j)) {
                i++;
                j++;
            } else {
                j = next[j];
            }
        }
        if (j >= lenSub)
            return i - j;
        return -1;
    }

    public static void getNext(String sub, int[] next) {
        next[0] = -1;
        next[1] = 0;
        int i = 2;
        int k = 0;

        for (; i < sub.length(); i++) {
            // p[i-1] == p[k]
            if (k == -1 || sub.charAt(i - 1) == sub.charAt(k)) {
                next[i] = k + 1;
                k++;
                i++;

            } else {
                k = next[k];
            }
        }
    }

    public static void main(String[] args) {
        System.out.println(KMP("ababcabcd", "ab", 3));
    }

}